<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
  </head>
  <body>
    <div id="app" a="1" b="2">
      <ul>
        <li>{{arr1}}</li>
      </ul>
    </div>

    <script src="/dist/vue.js"></script>
    <script>
      const vm = new Vue({
        el: "#app",
        data() {
          return {
            arr1: [[12,12]],
          };
        },
      });

      setTimeout(() => {
        vm.arr1[0].push(123)
      }, 1000)
    </script>
  </body>
</html>
